Electronics devices, such as computer systems or cellular phones, have become an integral part of many daily activities. These electronic devices rely on microelectronics for the key functions and features. Microelectronic products, such as semiconductor chips, are typically fabricated with defined production flows but with multiple, similarly configured components such as chambers, tools, and modules (e.g., a grouping of tools) operated in parallel. The intention is that production flows processed on different combinations of components will each produce batches of identical products. Typically, each of these products is made by utilizing a multitude of recipes, where each recipe may be thought of as a set of predefined process parameters required to effectuate a processing outcome.
Wafer processing systems and methods are widely used in the manufacture of semiconductors and integrated circuits. One particular type of wafer processing system utilizes chemical vapor deposition (CVD) to deposit films or layers on the surface of a substrate as a step in the manufacture of semiconductors and integrated circuits. For example, films may be deposited using low-pressure CVD (LPCVD) systems, atmospheric pressure CVD (APCVD) systems, or different types of plasma enhanced CVD (PECVD) systems. In general, all such systems employ a deposition chamber where certain injected gaseous chemicals react and deposit a layer of material on the surface of the substrate. Many types of materials may be deposited, with dielectrics such as oxides and nitrides being typical examples.
An important criterion when depositing films is the thickness uniformity of the film. It is desirable to achieve a film of substantially uniform thickness over the entire surface of the substrate. This goal becomes more difficult for larger diameter substrates. The temperature of the processes within the chamber plays an important role in the resulting film thickness. Thus, it is desirable to control the temperature and to promote substantially uniform deposition over the entire surface of the substrate.
To improve within-wafer uniformity with a fixed-temperature recipe for a batch-furnace CVD process, there are two common approaches. (1) Lower the average temperature of the process, improving uniformity at the expense of tool throughput, since lower-temperature recipes are generally much slower. (2) Increase the distance between wafers in the furnace, also reducing tool throughput, since fewer wafers could fit on the boat for each run.
Most LPCVD recipes keep the temperature target for a given furnace zone fixed during deposition in an effort to minimize variability. However, because the heater elements that heat the furnace are located outside the outer radius of the wafers, if the temperature changes, the change is effected first at the outer edge of the wafer. Thus, if the temperature at the heater element is ramped down during deposition, the cumulative deposition rate at the wafer edge decreases more than that at the wafer center. This allows one to modify the radial thickness profile of a film by changing the rate at which the temperature ramps, compensating for factors like gas depletion that generally give rise to within-wafer thickness variation.
Since the rate of the temperature ramp is proportional to the magnitude of the thickness profile change, one can adjust the temperature ramp rate to compensate for changes in radial thickness profile, regardless of its source. This sort of process adjustment conventionally requires a test run to confirm that ramp rate changes have the desired effect on uniformity. Since ramp rate changes affect the across-furnace variation as well as the within-wafer variation, multiple test run iterations are often required to adequately “tune” a ramped-temperature process. Furnace conditions can drift over time or change abruptly due to maintenance, which would require a new round of test runs to retarget the process, negatively impacting tool availability.
Thus, a need still remains for a wafer system to improve wafer uniformity without requiring extensive, non-productive test runs. In view of the ever-increasing commercial competitive pressures, coupled with the technical imperatives of improved die-to-die variation and improved production efficiency, it is critical that answers be found for these problems. Competitive pressures also demand lower costs alongside improved efficiencies and performance.
Solutions to these problems have been sought but prior developments have eluded those skilled in the art.